Hi,
For me, it seems as fast as OS 3, but the battery is draining a lot faster ! On OS3 i was never worrying about my battery, now around 6PM i'm around 30% which is not enough if i don't come home directly after work...
I have to say the new Siri Watchface is really really cool, it's the first watch face i use since i have my Apple Watch, i only used the 'utility' face with minimum details, which give a really minimal style to the watch, but the Siri is really nice, displayed the weather, calendar, and even a glance of one photo (i tried the face with one photo on, it's awfull but the small rectangle with a photo is so nice !) (but get rid of the stocks info, useless and ugly)...
For the battery maybe i use it more with the new face now, i feel like i have a new watch 🙂 ! But little by little, the laggyness is frustrating, and i'm not ready to spend 500$ on the new 4G yet... maybe next year